(Per)fluoropolyethers (PFPE) are fluorinated polymers comprising a straight or branched fully or partially fluorinated polyoxyalkylene chain that contains recurring units having at least one catenary ether bond and at least one fluorocarbon moiety. The most widespreadly known PFPE can be obtained by homopolymerization of hexafluoropropylene oxide (HFPO) or 2,2,3,3-tetrafluorooxetane and by photooxidation of tetrafluoroethylene (TFE) and/or hexafluoropropylene (HFP).
PFPE can be divided into non-functional and functional; the former comprise a PFPE chain whose ends bear (per)haloalkyl groups, while the latter comprise a PFPE chain having at least two ends, wherein at least one end comprises a functional group. Functional PFPEs, in particular mono- and bifunctional PFPE, i.e. those comprising a PFPE chain having two ends, wherein one or both end(s) bear(s) a functional group, have a variety of industrial uses, which depend on the structure and molecular weight of the PFPE chain and on the nature of the functional group. For example, mono- and bifunctional PFPE are used as ingredients or additives in lubricant compositions, coating compositions for imparting hydro-/oleo-repellence to substrates, or as intermediates or building blocks for the manufacture of other polymers.
Among functional PFPE, those bearing zwitterionic groups are known in the art.
For example, U.S. Pat. No. 6,225,367 B (NOVARTIS AG) 1 May 2001 relates to polymers comprising one or more PFPE units, in particular CF2CF2O and CF2O units, and one or more different charged units, including zwitterionic units, a process for their manufacture and mouldings composed of such polymers. The polymers are useful for the manufacture of biomedical devices, in particular for ophthalmic devices. The polymers disclosed in this document are obtained, for example, by copolymerizing one or more macromonomers comprising at least one PFPE unit with at least one polymerizable charged monomer or precursor thereof that may comprise a zwitterionic group. However, the description and the examples refer only to the PFPE macromonomers containing more than one PFPE units.
US 2001037001 A (NOVARTIS AG) 1 Oct. 2011 relates to a cross-linkable copolymers obtainable by:
(a) copolymerizing at least one hydrophilic monomer having one ethylenically unsaturated double bond and at least one crosslinker comprising two or more ethylenically unsaturated double bonds in the presence of a chain transfer agent having a functional group; and(b) reacting one or more functional groups of the resulting copolymer with an organic compound having an ethylenically unsaturated group.
A suitable crosslinker is a perfluoroalkyl polyether, for example a macromer of formula:Q-(PFPE-L)n-1-PFPE-Qwherein:                Q is a cross-linkable group;        L is a difunctional moiety able to react with hydroxyl;        n is equal to or higher than 1; and        PFPE is a perfluorinated polyether of formula:—OCH2CF2O(CF2CF2O)x(CF2O)yCF2CH2O—        
Suitable hydrophilic monomers to be reacted with the cross-linker include mono-ethylenically unsaturated compounds comprising a zwitterionic substituent.
The cross-linkable copolymers disclosed in this document are said to be useful for the manufacture of biomedical mouldings, in particular ophthalmic mouldings like contact lenses.
US 2005228120 A (COMMW SCIENT & IND RES) 13 Oct. 2013 discloses, inter alia, a polymer comprising one or more macromonomer PFPE units (in particular straight PFPE chains consisting of CF2CF2O and CF2O units) and one or more charged units, including zwitterionic units that can be comprised in aliphatic, cycloaliphatic or heterocylic moieties.
CHAN, G. Y. N., et al. Approaches to improving the biocompatibility of porous perfluoropolyethers for ophthalmic applications. Biomaterials. 2006, vol. 27, no. 8, p. 1287-1295. discloses (page 1288, par. “Perfluoropolyether (PFPE) membrane preparation”) a method for preparing PFPE membranes by photo-copolymerization of a zwitterionic monomer and a PFPE macromonomer comprising polymerizable groups. Thus, the polymer membranes contain more PFPE units and more zwitterionic units.
None of the above documents discloses mono- or bifunctional PFPE comprising one PFPE chain having zwitterionic groups at one or both ends of the chain.
WO 2010/009191 (3M INNOVATIVE PROPERTIES COMPANY) discloses compounds that have partially fluorinated polyether groups and/or fully fluorinated polyether groups with a low number (e.g., up to 4) continuous perfluorinated carbon atoms. The compounds may be useful, for example, as surfactants or surface treatments.